Results for pharmacokinetics
On this page:
 
Dictionary:

pharmacokinetics

  (fär'mə-kō-kə-nĕt'ĭks, -kī-) pronunciation
n. (used with a sing. verb)
  1. The process by which a drug is absorbed, distributed, metabolized, and eliminated by the body.
  2. The study of this process.
pharmacokinetic phar'ma·co·ki·net'ic adj.
 
 
Medical Dictionary: phar·ma·co·ki·net·ics
(fär'mə-kō-kə-nĕt'ĭks, -kī-)
n.
  1. The process by which a drug is absorbed, distributed, metabolized and eliminated by the body.
  2. The study of this process.
phar'ma·co·ki·net'ic adj.
 
Veterinary Dictionary: pharmacokinetics

The study of the movement of drugs in the body, including the processes of absorption, distribution, localization in tissues, biotransformation and excretion.

 
WordNet: pharmacokinetics
Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: the study of the action of drugs in the body: method and rate of excretion; duration of effect; etc.


 
Wikipedia: pharmacokinetics

Pharmacokinetics (in Greek: "pharmacon" meaning drug and "kinetikos" meaning putting in motion, the study of time dependency) is a branch of pharmacology dedicated to the determination of the fate of substances administered externally to a living organism. In practice, this discipline is applied mainly to drug substances, though in principle it concerns itself with all manner of compounds ingested or otherwise delivered externally to an organism, such as nutrients, metabolites, hormones, toxins, etc. Pharmacokinetics is often divided into several areas including, but not limited to, the extent and rate of Absorption, Distribution, Metabolism and Excretion. This sometimes is referred to as the ADME scheme.

Absorption is the process of a substance entering the body. Distribution is the dispersion or dissemination of substances throughout the fluids and tissues of the body. Metabolism is the irreversible transformation of substances and its daughter metabolites. Excretion is the elimination of the substances from the body. In rare cases, some drugs irreversibly accumulate in a tissue in the body.

Pharmacokinetics is often studied in conjunction with pharmacodynamics. So while pharmacodynamics explores what a drug does to the body, pharmacokinetics explores what the body does to the drug.

Pharmacokinetics is sometimes abbreviated as "PK".

Drug properties that influnce its pharmacokinetics

Partition coefficient

The partition or distribution coefficient (KD) is the ratio of concentrations of a compound in the two phases of a mixture of two immiscible solvents at equilibrium.[1]. It can influence the ADME properties (Absorption, Distribution, Metabolism, and Excretion) of the drug. When orally administered drugs are absorbed they must first pass through lipid bilayers in the intestinal epithelium (a process known as transcellular transport). For efficient transport, the drug must be hydrophobic enough to partition into the lipid bilayer, but not so hydrophobic, that once it is in the bilayer, it will not partition out again.[2]. The partition coefficient is dependent on the hydrophobic or hydrophilic properties of the drug.

Pharmacokinetic Analysis

Pharmacokinetic analysis is performed by noncompartmental (model independent) or compartmental methods. Noncompartmental methods estimate the exposure to a drug by estimating the area under the curve of a concentration-time graph. Compartmental methods estimate the concentration-time graph using kinetic models.

Noncompartmental PK Analysis

Noncompartmental PK analysis is highly dependent on estimation of total drug exposure. Total drug exposure is most often estimated by Area Under the Curve methods, with the trapezoidal rule (numerical differential equations) the most common area estimation method. Due to the dependence of the length of 'x' in the trapezoidal rule, the area estimation is highly dependent on the blood/plasma sampling schedule. That is, the closer your time points are, the closer the trapezoids are to the actual shape of the concentration-time curve.

Compartmental PK Analysis

Compartmental PK analysis uses kinetic models to describe and predict the concentration-time curve. PK compartmental models are often similar to kinetic models used in other scientific disciplines such as chemical kinetics and thermodynamics. The advantage of compartmental to noncompartmental analysis is the ability to predict the concentration at any time. The disadvantage is the difficulty in developing and validating the proper model. The simplest PK compartmental model is the one-compartmental PK model with IV bolus administration and first-order elimination.

Bioanalytical Methods

Bioanalytical methods are necessary to construct a concentration-time profile. Chemical techniques are employed to measure the concentration of drugs in biological matrix, most often plasma. Proper bioanalytical methods should be selective and sensitive.

Mass Spectrometry

Pharmacokinetics is often studied using mass spectrometry because of the complex nature of the matrix (often blood or urine) and the need for high sensitivity to observe low dose and long time point data. The most common instrumentation used in this application is LC-MS with a triple quadrupole mass spectrometer. Tandem mass spectrometry is usually employed for added specificity. Standard curves and internal standards are used for quantitation of usually a single pharmaceutical in the samples. The samples represent different time points as a pharmaceutical is administered and then metabolized or cleared from the body. Blank or t=0 samples taken before administration are important in determining background and insuring data integrity with such complex sample matrices. Much attention is paid to the linearity of the standard curve; however it is not uncommon to use curve fitting with more complex functions such as quadratics since the response of most mass spectrometers is less than linear across large concentration ranges.[3][4][5]

There is currently considerable interest in the use of very high sensitivity mass spectrometry for microdosing studies, which are seen as a promising alternative to animal experimentation.

See also

References

  1. ^ Leo A, Hansch C, and Elkins D (1971). "Partition coefficients and their uses". Chem Rev 71 (6): 525-616. DOI:10.1021/cr60274a001. 
  2. ^ Kubinyi H (1979). "Nonlinear dependence of biological activity on hydrophobic character: the bilinear model". Farmaco [Sci] 34 (3): 248-76. PMID 43264. 
  3. ^ Increasing Speed and Throughput When Using HPLC-MS/MS Systems for Drug Metabolism and Pharmacokinetic Screening, Y. Hsieh and W.A. Korfmacher, Current Drug Metabolism Volume 7, Number 5, 2006, Pp. 479-489
  4. ^ Covey TR, Lee ED, Henion JD. 1986. High-speed liquid chromatography/tandem mass spectrometry for the determination of drugs in biological samples. Anal Chem 58:2453-2460.
  5. ^ Thermospray liquid chromatography/mass spectrometry determination of drugs and their metabolites in biological fluids. Covey TR et al. Anal Chem. 1985 Feb;57(2):474-81

External Links


 
 

Join the WikiAnswers Q&A community. Post a question or answer questions about "pharmacokinetics" at WikiAnswers.

 

Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Medical Dictionary. The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company Read more
Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.  Read more
WordNet. WordNet 1.7.1 Copyright © 2001 by Princeton University. All rights reserved.  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Pharmacokinetics" Read more

Search for answers directly from your browser with the FREE Answers.com Toolbar!  
Click here to download now. 

Get Answers your way! Check out all our free tools and products.

On this page:   E-mail   print Print  Link  

 

Keep Reading

Mentioned In: